1. Field of the Invention
The present invention relates to novel organopolysiloxane compositions and matte paints formulated therefrom, and, more especially, to such compositions/paints comprised of methylphenylpolysiloxane resins, and specified amounts of finely divided aluminum and silica powders. Coatings can be produced from the subject compositions which have improved hardness when heated.
2. Description of the Prior Art
Organopolysiloxane resins pigmented with aluminum powder have been known since the beginning of the silicone art. Compare, in particular, U.S. Pat. Nos. 2,709,558, 2,743,192, 4,289,677, French Pat. Nos. 1,213,487, 1,387,725, 1,393,728, British Pat. Nos. 818,301, 1,179,127, German Pat. No. 2,046,385 and published Japanese Application Nos. 55/068,695 and 55/165,963.
Especially compare U.S. Pat. No. 2,743,192 and the Japanese Application No. 55/068,695, which describe the addition of inorganic fillers such as silicas to mixtures consisting of organopolysiloxane resins and aluminum powders.
More precisely, U. S. Pat. No. 2,743,192 relates to coating compositions comprising 100 parts of a methylphenylpolysiloxane resin which is soluble in organic solvents, 70 to 125 parts of a flaky aluminum pigment, 12 to 20%, based on the aluminum pigment, of a refractory filler principally selected from among titanium oxide, alumina, silica and zirconium oxide, and 60 to 300 parts of organic solvents. The aluminum pigment and the refractory filler consist of particles, a high proportion of which pass through sieves containing 325 mesh per inch. Example 4 illustrates the use of a silica having a mean particle diameter of 44 .mu.m; coatings produced from these compositions are said to have improved heat resistance.
With reference to Japanese Application No. 55/68,695, this also relates to coatings which have good thermal resistance and which are intended to protect printed circuits. These coatings are prepared from silicone resins combined with finely divided fillers such as titanium oxide, aluminum, clay, silica and talc. The examples provide little information concerning the nature of the silicone resins, or of their concentration within the commercial formulations employed; however, more detailed information is provided concerning the amounts of fillers added. Thus, Example 1 describes a composition continuing 3 parts of silica having a specific surface of 200 m.sup.2/ g, 10 parts of iron oxide, and 80 parts of a silicone resin, .times.400 and Example 2 describes a composition containing 25 parts of an aluminum paste and 69.4 parts of a silicone resin, KR 201.
U.S. Pat. No. 2,743,192 and Japanese Application No. 55/68,695 describe certain combinations of silicone resins with inorganic fillers and/or aluminum powder for the production of coatings having good thermal resistance. They do not describe any means to be used to provide coatings which retain good hardness when heated, that is to say, which are essentially devoid of thermoplasticity.
The elimination of thermoplasticity is much sought after in the case of nonadhesive coatings, based on silicone resins, which are deposited onto articles which are used when they are heated, such as cooking utensils. It is obvious that if the coatings are readily torn off, stripped or become unstuck or perforated, they are no longer useful to impart a non-adhesive nature to articles which are in continual contact with sticky or crust-forming products which are formed when food is being cooked. Serious need thus exists in this art for coatings which do not soften when heated, and which are cheap and easy to apply, especially in the field of nonadhesion to foodstuffs.